Hope for the blind

Sufferers from the little known eye condition of retinitis pigmentosa made the headlines when it was announced that an artificial retina had been implanted in the eyes of a number of blind persons with good results.

It is still too early to state that a cure for this condition has been found, but this news certainly brings hope to these persons who normally are destined to a dark future.

Research into the possibility of an artificial eye to restore vision to blind people has been carried out for several years in various countries, notably the United States and Germany.

The May 1996 issue of the IEEE Spectrum, the journal of the Institute of Electrical and Electronic Engineers was dedicated to bioelectronic vision, the search for prosthetics to give sight to the blind.

Various different areas of research were described with the aim of using electronics to replace the lost function of the natural organs of sight.

Devices included small television cameras mounted on glasses and transmitting optical signals to sensors inside the eyeball. Other researchers aim at replacing the eye completely by connecting the electronic camera directly to the area of the brain dedicated to vision.

The eye itself is in many ways similar to a camera with the lens focusing the image on the retina at the back of the eyeball from where it is transmitted to the brain through the optic nerve. Any part of the system which malfunctions may cause reduced vision or blindness.

Glasses only correct refractive defects of the eye, while other conditions may exist which may or may not be curable. Cataract, for example, where the lens of the eye becomes opaque, causing blindness, can be cured by removing the lens of the eye by an operation and replacing it with a lens made of perspex implanted in the eye.

Loss of clarity may also effect the cornea, the hard outer surface of the eyeball. This is sometimes cured by means of a corneal graft, and eye banks exist where corneas for donors who died in an accident may be used for transplanting in patients with such conditions.

No such transplant is however possible for the retina, the light sensitive part of the eye. This consists of a hundred to two hundred million receptors, which are specialised light sensitive cells. The optic nerve transmitting the optical information from the retina to the brain is made up of a million neurons. Transplanting a complete eye would require the joining of these million neurons, and is considered impossible with present knowledge.

The retina itself is subject to various disorders. The blood supply to this organ may be defective or the retina itself may become detached and the photosensitive layer separated from the neural layer. The latter may in some cases be repaired but once the damage is done it cannot be reversed. Persons blinded by diabetes or by glaucoma have undergone irreversible damage of the retina.

Retinitis pigmentosa (RP) is a group of diseases where there is a progressive degeneration of the photoreceptor cells of the retina. It is gene related and progresses inexorably from the first symptoms of night blindness to tunnel vision and loss of acuity until at some point little or no vision remains. There is no cure for this disease, and no treatment which slows down its progress.

There are several varieties, some appearing in the teens while others will become apparent when the sufferer is in his thirties. They are caused by disorders in different genes, some of which have been discovered. Some varieties run in families, while others are caused by recessive genes and appear in persons with no known relations with the condition.

The disease attacks only selected photoreceptor cells. These cells, known as the rods from their shape, start degenerating and dead cells are not replaced. For some unknown reason the other receptors in the retina also stop functioning, even though they are undamaged. Thus, if a way can be found to replace the dead photoreceptors, the rest of the apparatus is there ready to perform its function.

The idea of Dr Alan Chow and his brother Vincent, founders of the Optobionics Corporation, is to implant a silicon chip consisting of some 3,500 microscopic solar cells on the retinal wall. This will convert light into electrical impulses which stimulate the other layers of the retina into sending a signal to the brain in the same manner as in a normal retina. The Artificial Silicon Retina, as it is called, is only 2 mm in diameter and a thousand of an inch thick and is inserted into the eyeball by means of a relatively simple operation.

This is an amazingly simple concept compared with other attempts in making an artificial eye. Such alternative projects include external television cameras which require a mechanism to move the camera with the movements of the eyeball, and to adjust for varying light. The camera is connected to an implant inside the retina by means of an optic fibre, and inserting the implant requires the flushing out of the inside of the eyeball.

The simplicity of the Chow implant makes it suitable only for a limited number of patients, notably those with retinitis pigmentosa who still possess an undamaged retina except for the defective photoreceptors. Whether it is effective is another question. The chip was first implanted in animals to ensure that it would be tolerated. This phase was successful, and the next stage was to implant it into humans.

This was done in June 2000, and the event was published on the internet. However since then the website has been reticent about the results, until last week it was announced that good results had been obtained. The news was limited and the Chow brothers promised to divulge further information when the results are published in a scientific publication.

There have been doubts about the effectiveness of the method. Researchers working on competing projects have stated that it is not possible for the chip to receive sufficient light to power the electronic circuit, especially in low light conditions. In contrast other artificial retinas have an external power source.

The present reports are incomplete. One report states the patients can only see simple patterns and cannot as yet recognise a face. Another report states that a person with the implant was surprised to see his face wrinkled, as it had been 20 years since he last saw it in a mirror.

RP sufferers, who are estimated to be about 200 in Malta, eagerly await further news. The Chow brothers state that their chip will be in production in five years time. The simplicity of the concept should be such that once it is established the implant will have widespread use.

On the other hand, miracle cures for RP have time and again been announced, only to give false hope to the persons who undergo the treatment for this incurable disease. One thing is certain: millions are being spent in research and the artificial eye in one form or another will one day be a reality. In the words of a leading researcher, we do no longer ask if but when a cure will be found for retinitis pigmentosa.